The failure to detect, find, and correct minor roof deterioration in the earliest stages is considered the greatest cause of premature roof failure. This is particularly true of roofing materials applied on low-slope or flat roofs. Costly roofing problems are often the result of design deficiencies or faulty application of the roof system. Even when properly designed and applied, all roofing materials deteriorate from the contraction and expansion of roof decks and natural aging processes.
Several methods have been used to try and locate roof leaks after they have occurred. Electric capacitance meters identify leaks using a low-frequency method that measures dielectric constant changes in the roofing material as a result of moisture below the membrane. Infrared cameras allow technicians to scan roof surfaces for temperature differentials that signify moist areas through changes in thermal conductivity or evaporation. These methods are typically used in forensic analysis only after significant leakage has occurred.
Electric field mapping uses a wire loop around the perimeter of the roof surface to introduce an electric potential between the structural deck and a selected roof area which is sprayed with water. The electric field potential caused by a conductive path to any roof membrane damage is then located using a voltmeter and a pair of probes.
U.S. Pat. No. 4,565,965 issued Jan. 21, 1986 to Geesen discloses an electric field mapping arrangement for detecting leaks in flat roofs in which electrical pulses are transmitted through the moisture in the leak to the roof edge. The roof is then scanned by a pulse sensor and hand-held probe rods to find the leak by locating the maximum amplitude. The disclosure of this prior patent is incorporated herein by reference.
The method as described by Geesen requires considerable experience and careful placement of a wire loop around the perimeter of the area to be tested. A pair of hand held probes are positioned on the surface to be tested while the operator simultaneously views a meter dial reading. A low frequency dc pulse generator is used to energize the area under test. The locating signal is thereby switched on and off at regular intervals which allows adjustment of the “0” set calibration between pulses when needed. This results in a charging current rush at the beginning of every pulse. On larger decks the charging current is large enough to cause a false reading on the meter thus indicating a roof membrane defect where none exists. The placing and spacing of the probes require care in both position and spacing to avoid erroneous readings.